从json文件BufferedReader读取数据仅返回null

Question

I'm currently learning android with a books called "Android Programming - The Big Nerd Ranch Guide". As a part of a learning project we create Json serializer for saving and loading data. Writing the file appearently works fine, and I get no error messages on the Logcat. After I terminate the app and recreate it, the data loader is called and raises the following exception:

org.json.JSONException: End of input at character 0

I've looked for this issue online and figured it's probably because the BufferedReader returns an empty response. I've checked and indeed it is the case. For simplicity sake, I've temporarily put a BufferedReader into the saving function and tried reading the info I've just saved into the file, and still the BufferedReader returns only null.

public void saveCrimes(ArrayList<Crime>crimes)
    throws JSONException, IOException {
    JSONArray array = new JSONArray();
    for(Crime c: crimes)
        array.put(c.toJSON());
    Writer writer = null;
    try {
        OutputStream out = mContext.openFileOutput(mFileName, Context.MODE_PRIVATE);
        writer = new OutputStreamWriter(out);
        writer.write(array.toString());
        Log.d(TAG, array.toString());
    } finally {
        if(writer == null)
            writer.close();
    }
    // Extracting the data
    BufferedReader bufferedReader = null;
    try {
        InputStream inputStream = mContext.openFileInput(mFileName);
        bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
        if (bufferedReader.readLine() == null)
            Log.d(TAG, "WHY GOD WHYYYYYYY");
    }catch (IOException e){

    }
}

(The two log messages from the code, the first one displays the data that is in the JsonArray I'm using)

D/CriminalIntentJSONSerializer: [{"date":"Mon May 14 17:33:08 GMT+00:00 2018","id":"97fe9532-991f-4352-9de1-602fa8dfa93e","isSolved":true,"title":""}] D/CriminalIntentJSONSerializer: WHY GOD WHYYYYYYY

Would love to hear your insight.

Answer 1

BufferedReader bufferedReader = null;
try {
    InputStream inputStream = mContext.openFileInput(mFileName);
    bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
    if (bufferedReader.readLine() == null)
        Log.d(TAG, "WHY GOD WHYYYYYYY");
}catch (IOException e){

}

Ok. you've created your BufferedReader bufferedReader = null; What happens when yuou say bufferedReader = new BufferedReader(anything) ...Well...it can't call a new instance the same thing that's already been declared...in fact, it's already been instantiated as null. So you can't create a new instance of the same name.

Try deleting the line where you point it at null. Then, substitute BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream)); for the original declaration in your try block

Answer 2

Try to check if mFilename is empty on second try-catch , usually in Android instance disappear easily.

PD: I advise you choice another JSON library to manipulte JSON files, they are lightweight and easy-to-use .

== Edit ==

Have you added writing and reading permissions on AndroidManifest? If answer is "there it is" try to debug app step-by-step looking for variables and in-variables for checking existence of values.

Could be file isn't writing itself or it's writing empty.

Error basically is empty string or non-format JSON-like:

""
"[{"a": "abdc", "b": "jef2","

Paying attention to BufferedReader because it read lines each and you need all file and then join into string variable.

Also, try to use android file explorer that come in AndroidStudio. There you can explore files, logs and database files and export them to your specific folders (Documents, Downloads, etc). Generally files written by app are stored in data -> <com.your.app.package> .